In the field of optical urethane resins and plastic lenses utilizing them, the resin obtained by reacting a halogen-containing compound having more than 2 hydroxyl groups with an isocyanate compound (JP Kokai S-58-164615/1983), the resin obtained by reacting a mercapto group-containing compound with an isocyanate compound (JP Kokai S-60-199016/1985) and a polyurethane resin added with a phenolic stabilizer (JP Kokai H-5-78441/1993), among others, have been proposed in many patent applications, all alluding to optical lenses of reduced coloration, high total light transmission and low optical distortion.
With regard to optical distortion, however, no drastic removal remains to be attained and because of the high rejection rate of products, the manufacturing conditions have to be corrected from time to time.